1. Field of the Invention
The present invention relates to a closed loop power control method in a mobile communication system, and more particularly to a wind-up power control method and apparatus in a mobile communication system.
2. Description of the Related Art
ln general, in a wideband code division multiple access (WCDMA) mobile communication system, when a mobile terminal passes through a tunnel, etc., an error occurs in a channel due to a sudden decrease in a received power. Therefore, to compensate for the degraded channel, the mobile terminal transmits a command to a corresponding base station requesting the base state sharply increase its transmission power. However, even though this improves the possibility the terminal will receive the channel information without error, the increase in base station power negatively affects other mobile terminals.
To solve this problem, the mobile communication. system uses a wind-up power control algorithm. For example, when a number of times a mobile station has issued a command requesting the base station increase its power is equal to or larger than a particular number, the mobile terminal initiates the wind-up power control algorithm or process.
In the wind-up power control algorithm, a maximum base station transmission power is set a particular level. In more detail; a target power value (target signal to interference ratio (SIR)) of a downlink channel is fixed. Therefore, even if an error occurs in the downlink channel received by the mobile station, the base station does not increase the power intensity beyond the fixed target SIR.
However, the fixed target SIR is more than what is required to provide a general quality of service (QoS) for the mobile terminal operating in a normal environment. Thus, in the wind-up power control algorithm, after the mobile terminal passes through the tunnel, for example, the mobile terminal cancels the higher target SIR and uses an appropriate lower target SIR. Further, when releasing the wind-up power control process, the mobile terminal decreases the higher target SIR using a SIR down step size. That is, the higher SIR value is decreased in smaller steps rather than changing the higher SIR value to the lower SIR value in one single step.